US20230329126A1 - Quantum bit circuit, quantum computer, method for manufacturing quantum bit circuit - Google Patents

Quantum bit circuit, quantum computer, method for manufacturing quantum bit circuit Download PDF

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US20230329126A1
US20230329126A1 US18/311,261 US202318311261A US2023329126A1 US 20230329126 A1 US20230329126 A1 US 20230329126A1 US 202318311261 A US202318311261 A US 202318311261A US 2023329126 A1 US2023329126 A1 US 2023329126A1
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majorana
carrier
region
particle
edge
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Manabu Ohtomo
Kenichi Kawaguchi
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Fujitsu Ltd
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/10—Junction-based devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/10—Junction-based devices
    • H10N60/12—Josephson-effect devices
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
    • G06N10/40—Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D48/00—Individual devices not covered by groups H10D1/00 - H10D44/00
    • H10D48/383—Quantum effect devices, e.g. of devices using quantum reflection, diffraction or interference effects
    • H10D48/3835—Semiconductor qubit devices comprising a plurality of quantum mechanically interacting semiconductor quantum dots, e.g. Loss-DiVincenzo spin qubits
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/01—Manufacture or treatment
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/01—Manufacture or treatment
    • H10N60/0912—Manufacture or treatment of Josephson-effect devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/80—Constructional details
    • H10N60/805—Constructional details for Josephson-effect devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N69/00—Integrated devices, or assemblies of multiple devices, comprising at least one superconducting element covered by group H10N60/00
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic

Definitions

  • the present disclosure relates to a quantum bit circuit, a quantum computer, and a method for manufacturing the quantum bit circuit.
  • a quantum computer using Majorana particles has been studied.
  • As a structure for generating the Majorana particles for example, the following two types of techniques have been proposed. One is a technique using a one-dimensional semiconductor nanowire, and another one is a technique using a two-dimensional topological insulator.
  • Patent Document 1 Japanese Laid-open Patent Publication No. 2013-247267
  • Patent Document 2 Japanese National Publication of International Patent Application No. 2020-511780
  • Non-Patent Document 1 Coulomb-assisted braiding of Majorana fermions in a Josephson junction array, New Journal of Physics 14, 035019 (2012)
  • Non-Patent Document 2 Minimal circuit for a flux-controlled Majorana qubit in a quantum spin-Hall insulator, Physica Scripta T164, 014007 (2015)
  • Non-Patent Document 3 Direct visualization of a two-dimensional topological insulator in the single-layer 1T′-WTe2, Physical Review B 96, (2017).
  • a quantum bit circuit including: a first Majorana carrier extended in a first direction; and a second Majorana carrier extended in a second direction that intersects with the first direction, wherein the First Majorana carrier includes a first region where a Majorana particle is able to exist, in a portion that overlaps the second Majorana carrier in plan view, the second Majorana carrier includes a second region where a Majorana particle is able to exist, in a portion that overlaps the first Majorana carrier in plan view, and the Majorana particle in the first region and the Majorana particle in the second region are exchangeable.
  • FIG. 1 is a top view of a quantum bit circuit according to a first embodiment
  • FIG. 2 is an enlarged view illustrating a part in FIG. 1 ;
  • FIG. 3 is a cross-sectional diagram (part 1 ) illustrating the quantum bit circuit according to the first embodiment
  • FIG. 4 is a cross-sectional diagram (part 2 ) illustrating the quantum bit circuit according to the first embodiment
  • FIG. 5 is a diagram illustrating an example of an operation of the quantum bit circuit according to the first embodiment
  • FIG. 6 is a top view (part 1 ) illustrating a method for manufacturing the quantum bit circuit according to the first embodiment
  • FIG. 7 is a top view (part 2 ) illustrating the method for manufacturing the quantum bit circuit according to the first embodiment
  • FIG. 8 is a top view (part 3 ) illustrating the method for manufacturing the quantum bit circuit according to the first embodiment
  • FIG. 9 is a top view (part 4 ) illustrating the method for manufacturing the quantum bit circuit according to the first embodiment
  • FIG. 10 is a top view (part 5 ) illustrating the method for manufacturing the quantum bit circuit according to the first embodiment
  • FIG. 11 is a top view (part 6 ) illustrating the method for manufacturing the quantum bit circuit according to the first embodiment
  • FIG. 12 is a top view (part 7 ) illustrating the method for manufacturing the quantum bit circuit according to the first embodiment
  • FIG. 13 is a top view (part 8 ) illustrating the method for manufacturing the quantum bit circuit according to the first embodiment
  • FIG. 14 is a top view illustrating a quantum bit circuit according to a second embodiment
  • FIG. 15 is an enlarged view illustrating a part in FIG. 14 ;
  • FIG. 16 is a cross-sectional diagram (part 1 ) illustrating the quantum bit circuit according to the second embodiment
  • FIG. 17 is a cross-sectional diagram (part 2 ) illustrating the quantum bit circuit according to the second embodiment
  • FIG. 18 is a band diagram illustrating an example of a valence band and a conduction band of a laminate
  • FIG. 19 is a diagram illustrating a change in a tunnel barrier
  • FIG. 20 is a diagram illustrating an example of an operation of the quantum bit circuit according to the second embodiment.
  • FIG. 21 is a diagram illustrating a method (part 1 ) for manufacturing the quantum bit circuit according to the second embodiment
  • FIG. 22 is a diagram illustrating the method (part 2 ) for manufacturing the quantum bit circuit according to the second embodiment
  • FIG. 23 is a diagram illustrating the method (part 3 ) for manufacturing the quantum bit circuit according to the second embodiment
  • FIG. 24 is a diagram illustrating the method (part 4 ) for manufacturing the quantum bit circuit according to the second embodiment
  • FIG. 25 is a diagram illustrating the method (part 5 ) for manufacturing the quantum bit circuit according to the second embodiment
  • FIG. 26 is a diagram illustrating the method (part 6 ) for manufacturing the quantum bit circuit according to the second embodiment
  • FIG. 27 is a diagram illustrating the method (part 7 ) for manufacturing the quantum bit circuit according to the second embodiment
  • FIG. 28 is a diagram illustrating the method (part 8 ) for manufacturing the quantum bit circuit according to the second embodiment
  • FIG. 29 is a diagram illustrating the method (part 9 ) for manufacturing the quantum bit circuit according to the second embodiment
  • FIG. 30 is a partially transparent top view illustrating a quantum bit circuit according to a third embodiment
  • FIG. 31 is a cross-sectional diagram (part 1 ) illustrating the quantum bit circuit according to the third embodiment
  • FIG. 32 is a cross-sectional diagram (part 2 ) illustrating the quantum bit circuit according to the third embodiment
  • FIG. 33 is a cross-sectional diagram (part 3 ) illustrating the quantum bit circuit according to the third embodiment
  • FIG. 34 is a cross-sectional diagram (part 4 ) illustrating the quantum bit circuit according to the third embodiment.
  • FIG. 35 is a diagram illustrating a quantum computer.
  • An object of the present disclosure is to provide a quantum bit circuit that can manufacture a structure that can be easily controlled, with a high yield, a quantum computer, and a method for manufacturing the quantum bit circuit.
  • FIG. 1 is a top view of the quantum bit circuit according to the first embodiment.
  • FIG. 2 is an enlarged view illustrating a part in FIG. 1 .
  • FIGS. 3 and 4 are cross-sectional diagrams illustrating the quantum bit circuit according to the first embodiment.
  • FIG. 3 corresponds to a cross-sectional diagram taken along a line III-III in FIG. 1 .
  • FIG. 4 corresponds to a cross-sectional diagram taken along a line IV-IV in FIG. 1 .
  • a quantum bit circuit 1 includes a substrate 110 , a lower Majorana carrier 121 extending in an X-axis direction, and an upper Majorana carrier 122 extending in a Y-axis direction.
  • the substrate 110 is, for example, an insulating substrate such as an alumina substrate or a sapphire substrate.
  • the X-axis direction and the Y-axis direction are directions orthogonal to a Z-axis direction perpendicular to a surface of the substrate 110 .
  • the Y-axis direction intersects with the X-axis direction, and for example, the X-axis direction and the Y-axis direction are orthogonal to each other.
  • the X-axis direction is an example of a first direction
  • the Y-axis direction is an example of a second direction.
  • Majorana carrier means to be a substance including a topological insulator bearing Majorana particle.
  • the lower Majorana carrier 121 is, for example, a two-dimensional topological insulator layer, and includes a first edge 161 and a third edge 163 extending in the X-axis direction. The first edge 161 is positioned on a ⁇ Y side of the third edge 163 .
  • the lower Majorana carrier 121 may be formed of a single two-dimensional topological insulator or may be formed by laminating a plurality of two-dimensional topological insulators.
  • a material of the lower Majorana carrier 121 is, for example, tungsten ditelluride (WTe2).
  • WTe2 tungsten ditelluride
  • the plurality of lower Majorana carriers 121 is arranged side by side in the Y-axis direction.
  • the lower Majorana carrier 121 is an example of a first Majorana carrier.
  • the upper Majorana carrier 122 is, for example, a two-dimensional topological insulator layer and includes a second edge 162 and a fourth edge 164 extending in the Y-axis direction.
  • the second edge 162 is positioned on a ⁇ X side of the fourth edge 164 .
  • the upper Majorana carrier 122 may be formed of a single two-dimensional topological insulator or may be formed by laminating a plurality of two-dimensional topological insulators.
  • a material of the upper Majorana carrier 122 is, for example, tungsten ditelluride (WTe2).
  • WTe2 tungsten ditelluride
  • the plurality of upper Majorana carriers 122 is arranged side by side in the X-axis direction.
  • the upper Majorana carrier 122 is an example of a second Majorana carrier.
  • a lower s-wave superconductor layer 131 in contact with a lower surface of the lower Majorana carrier 121 is provided.
  • the lower s-wave superconductor layer 131 is provided along the first edge 161 and the third edge 163 , for each region overlapping the upper Majorana carrier 122 in plan view.
  • An end of each lower s-wave superconductor layer 131 in the X-axis direction is separated from the second edge 162 and the fourth edge 164 of the upper Majorana carrier 122 in plan view.
  • the lower s-wave superconductor layer 131 is, for example, an Al layer.
  • a lower s-wave superconductor layer 132 in contact with an upper surface of the lower Majorana carrier 121 is provided.
  • the lower s-wave superconductor layer 132 is provided along the first edge 161 and the third edge 163 , for each region between the upper Majorana carriers 122 adjacent to each other in plan view.
  • An end of each lower s-wave superconductor layer 132 in the X-axis direction is separated from the second edge 162 and the fourth edge 164 of the upper Majorana carrier 122 in plan view.
  • the lower s-wave superconductor layer 132 is, for example, an Al layer.
  • the lower s-wave superconductor layers 131 and 132 are examples of a first s-wave superconductor layer.
  • An upper s-wave superconductor layer 133 in contact with an upper surface of the upper Majorana carrier 122 is provided.
  • the upper s-wave superconductor layer 133 is provided along the second edge 162 and the fourth edge 164 , for each region overlapping the lower Majorana carrier 121 and each region between lower Majorana carriers 121 adjacent to each other, in plan view.
  • An end of the upper s-wave superconductor layer 133 in the X-axis direction is separated from the first edge 161 and the third edge 163 of the lower Majorana carrier 121 in plan view.
  • the upper s-wave superconductor layer 133 is, for example, an Al layer.
  • the upper s-wave superconductor layer 133 is an example of a second s-wave superconductor layer.
  • An etching stopper 140 is provided between the lower Majorana carrier 121 and the upper Majorana carrier 122 .
  • a material of the etching stopper 140 is, for example, graphene or graphite. In a case where the material of the etching stopper 140 is graphite, the thickness thereof is preferable as thin as possible, and is preferable to be equal to or less than five nm, for example. As described later, this is because Majorana particles tunnel through the etching stopper 140 between the lower Majorana carrier 121 and the upper Majorana carrier 122 .
  • Wiring is individually coupled to the lower s-wave superconductor layer 131 , the lower s-wave superconductor layer 132 , and the upper s-wave superconductor layer 133 .
  • the Majorana particles can exist in a portion between the lower s-wave superconductor layer 131 and the lower s-wave superconductor layer 132 adjacent to each other at the first edge 161 in plan view and a portion between the lower s-wave superconductor layer 131 and the lower s-wave superconductor layer 132 adjacent to each other at the third edge 163 in plan view. Then, for example, in these portions where the Majorana particles can exist, a portion of the first edge 161 overlapping the second edge 162 functions as a first region 171 , and a portion of the third edge 163 overlapping the second edge 162 functions as a third region 173 .
  • a portion of the first edge 161 overlapping the fourth edge 164 functions as a fifth region 175
  • a portion of the third edge 163 overlapping the fourth edge 164 functions as a seventh region 177 .
  • the Majorana particles can exist in a portion between the two upper s-wave superconductor layers 133 adjacent to each other at the second edge 162 in plan view and a portion between the two upper s-wave superconductor layers 133 adjacent to each other at the fourth edge 164 in plan view. Then, for example, in these portions where the Majorana particles can exist, a portion of the second edge 162 overlapping the first edge 161 functions as a second region 172 , and a portion of the fourth edge 164 overlapping the first edge 161 functions as a sixth region 176 .
  • a portion of the second edge 162 overlapping the third edge 163 functions as a fourth region 174
  • a portion of the fourth edge 164 overlapping the third edge 163 functions as an eighth region 178 .
  • the Majorana particles existing in the first region 171 and the Majorana particles existing in the second region 172 can pass through the etching stopper 140 by a tunnel effect and interact with each other. Therefore, both Majorana particles can be regarded as the same Majorana particle. The same applies to a pair of the third region 173 and the fourth region 174 , a pair of the fifth region 175 and the sixth region 176 , and a pair of the seventh region 177 and the eighth region 178 .
  • the Majorana particles generated in the lower Majorana carrier 121 and the Majorana particles generated in the upper Majorana carrier 122 can easily interact with each other. Furthermore, as described later, such a structure can be manufactured with a high yield, with alignment accuracy of a typical semiconductor process.
  • the Majorana particles can be exchanged between the first region 171 and the fifth region 175 and between the third region 173 and the seventh region 177 adjacent to each other, with the lower s-wave superconductor layers 131 and 132 interposed therebetween.
  • the Majorana particles can be exchanged between the second region 172 and the fourth region 174 and between the sixth region 176 and the eighth region 178 adjacent to each other, with the upper s-wave superconductor layer 133 interposed therebetween.
  • the quantum bit circuit 1 eight Majorana particles can be generated in a region where the lower Majorana carrier 121 and the upper Majorana carrier 122 overlap in plan view. Therefore, Majorana quantum bits can be accumulated at high density. Furthermore, the Majorana quantum bits can be regularly accumulated in a grid-like pattern, and wiring or the like can be easily designed.
  • FIG. 5 is a diagram illustrating an example of the operation of the quantum bit circuit according to the first embodiment.
  • Circles in FIG. 5 indicate Majorana particles in the regions 171 to 178 .
  • a line segment indicated by a broken line indicates that an s-wave superconductor layer is in a state where the Majorana particles cannot be exchanged
  • a line segment indicated by a solid line indicates that the s-wave superconductor layer is in a state where the Majorana particles can be exchanged.
  • the Majorana particles are exchanged between the two fifth regions 175 adjacent to each other with the first region 171 interposed therebetween in the X-axis direction.
  • a Majorana particle ⁇ 1 generated in one fifth region 175 and a Majorana particle ⁇ 4 generated in another fifth region 175 are exchanged via a Majorana particle ⁇ 2 generated in the first region 171 between these fifth regions 175 through charging.
  • FIGS. 6 to 13 are top views illustrating the method for manufacturing the quantum bit circuit according to the first embodiment.
  • the lower s-wave superconductor layer 131 is formed on the substrate 110 .
  • the lower s-wave superconductor layer 131 can be formed by a deposition method, for example.
  • a two-dimensional topological insulator layer 121 X is provided on the substrate 110 so as to cover the lower s-wave superconductor layer 131 .
  • the two-dimensional topological insulator layer 121 X can be provided, for example, by separately growing the two-dimensional topological insulator layer 121 X on a growth substrate (not illustrated) and transferring the two-dimensional topological insulator layer 121 X from the growth substrate.
  • the two-dimensional topological insulator layer 121 X may be formed on the substrate 110 .
  • the plurality of lower Majorana carriers 121 is formed by processing the two-dimensional topological insulator layer 121 X.
  • RIE reactive ion etching
  • etching gas for example, fluorocarbon gas is used.
  • an etching stopper 140 X is provided above the substrate 110 so as to cover the lower Majorana carrier 121 .
  • the etching stopper 140 X can be provided, for example, by separately growing the etching stopper 140 X on a growth substrate (not illustrated) and transferring the etching stopper 140 X from the growth substrate.
  • a two-dimensional topological insulator layer 122 X is provided on the etching stopper 140 X.
  • the two-dimensional topological insulator layer 122 X can be provided, for example, by separately growing the two-dimensional topological insulator layer 122 X on a growth substrate (not illustrated) and transferring the two-dimensional topological insulator layer 122 X from the growth substrate.
  • the two-dimensional topological insulator layer 122 X may be formed on the etching stopper 140 X.
  • the plurality of upper Majorana carriers 122 is formed by processing the two-dimensional topological insulator layer 122 X.
  • the RIE is performed.
  • etching gas for example, fluorocarbon gas is used.
  • the lower Majorana carrier 121 is protected by the etching stopper 140 X.
  • the etching stopper 140 is formed between the lower Majorana carrier 121 and the upper Majorana carrier 122 .
  • the RIE is performed.
  • As etching gas for example, oxygen gas is used.
  • the lower s-wave superconductor layer 132 is formed on the lower Majorana carrier 121
  • the upper s-wave superconductor layer 133 is formed on the upper Majorana carrier 122 .
  • the lower s-wave superconductor layer 132 and the upper s-wave superconductor layer 133 can be formed by the deposition method, for example.
  • wiring (not illustrated) or the like that is individually coupled to the lower s-wave superconductor layer 131 , the lower s-wave superconductor layer 132 , and the upper s-wave superconductor layer 133 is formed.
  • the quantum bit circuit 1 according to the first embodiment can be manufactured.
  • both of the lower s-wave superconductor layer 131 and the lower s-wave superconductor layer 132 may have contact with the lower surface of the lower Majorana carrier 121
  • both of the lower s-wave superconductor layer 131 and the lower s-wave superconductor layer 132 may have contact with the upper surface of the lower Majorana carrier 121 .
  • FIG. 14 is a top view of a quantum bit circuit according to the second embodiment.
  • FIG. 15 is an enlarged view illustrating a part in FIG. 14 .
  • FIGS. 16 and 17 are cross-sectional diagrams illustrating the quantum bit circuit according to the second embodiment.
  • FIG. 16 corresponds to a cross-sectional diagram taken along a line XVI-XVI in FIG. 14 .
  • FIG. 17 corresponds to a cross-sectional diagram taken along a line XVII-XVII in FIG. 14 .
  • a quantum bit circuit 2 includes a substrate 110 , a lower Majorana carrier 121 , an upper Majorana carrier 122 , a lower s-wave superconductor layer 131 , a lower s-wave superconductor layer 132 , and an upper s-wave superconductor layer 133 .
  • an etching stopper 241 , an etching stopper 242 , and a semiconductor layer 250 are provided between the lower Majorana carrier 121 and the upper Majorana carrier 122 .
  • the etching stopper 241 is provided between the lower Majorana carrier 121 and the semiconductor layer 250
  • the etching stopper 242 is provided between the semiconductor layer 250 and the upper Majorana carrier 122 .
  • a material of the etching stoppers 241 and 242 is, for example, graphene or graphite.
  • the thickness thereof is preferable as thin as possible, and is preferable to be equal to or less than five nm, for example. This is because Majorana particles tunnel through the etching stoppers 241 and 242 between the lower Majorana carrier 121 and the upper Majorana carrier 122 .
  • a material of the semiconductor layer 250 is, for example, a two-dimensional semiconductor such as tin diselenide (SnSe2).
  • a conductivity type of the semiconductor layer 250 is not limited, and for example, may be an intrinsic semiconductor or an n-type semiconductor.
  • the semiconductor layer 250 may be configured from a single two-dimensional semiconductor or may be configured by laminating a plurality of two-dimensional semiconductors.
  • the semiconductor layer 250 is an example of a tunnel barrier layer.
  • a lower electrode 251 is provided between the lower s-wave superconductor layers 131 that are adjacent to each other in an X-axis direction. Similarly to the lower s-wave superconductor layer 131 , the lower electrode 251 is covered with the lower Majorana carrier 121 . For example, the lower electrode 251 is provided in a region that does not overlap the upper Majorana carrier 122 in plan view. The lower electrode 251 is provided, for example, in each of the vicinity of a first region 171 , the vicinity of a third region 173 , the vicinity of a fifth region 175 , and the vicinity of a seventh region 177 .
  • an upper electrode 252 is provided on the upper Majorana carrier 122 .
  • the upper electrode 252 is provided, for example, in each of the vicinity of a second region 172 , the vicinity of a fourth region 174 , the vicinity of a sixth region 176 , and the vicinity of an eighth region 178 .
  • a power supply 253 is provided that applies a voltage between the lower electrode 251 and the upper electrode 252 respectively provided in the vicinity of the first region 171 and the vicinity of the second region 172 overlapping each other.
  • Another power supply 253 is provided that applies a voltage between the lower electrode 251 and the upper electrode 252 respectively provided in the vicinity of the third region 173 and the vicinity of the fourth region 174 overlapping each other.
  • Still another power supply 253 is provided that applies a voltage between the lower electrode 251 and the upper electrode 252 respectively provided in the vicinity of the fifth region 175 and the vicinity of the sixth region 176 overlapping each other.
  • Yet another power supply 253 is provided that applies a voltage between the lower electrode 251 and the upper electrode 252 respectively provided in the vicinity of the seventh region 177 and the vicinity of the eighth region 178 overlapping each other.
  • a laminated film of the etching stopper 241 , the semiconductor layer 250 , and the etching stopper 242 exists between the lower Majorana carrier 121 and the upper Majorana carrier 122 .
  • FIG. 18 an example of a band diagram of a valence band and a conduction band of a laminate of the lower Majorana carrier 121 , the etching stopper 241 , the semiconductor layer 250 , the etching stopper 242 , and the upper Majorana carrier 122 is illustrated in FIG. 18 .
  • each of the lower Majorana carrier 121 and the upper Majorana carrier 122 includes the same WTe2
  • the etching stoppers 241 and 242 include graphene
  • the semiconductor layer 250 includes four-layer SnSe2.
  • a tunnel barrier exists between the Majorana particle generated in the lower Majorana carrier 121 and the Majorana particle generated in the upper Majorana carrier 122 .
  • a height of this tunnel barrier can be adjusted according to a magnitude of a gate voltage to be applied from the power supply 253 . For example, by applying the gate voltage, it is possible to change a band of the semiconductor layer 250 and lower the tunnel barrier so as to induce a tunnel effect.
  • FIG. 19 is a diagram illustrating a change in a tunnel barrier.
  • changes in a valence band EV and a conduction band EC of the semiconductor layer 250 are illustrated together with a Fermi level EF.
  • a gate voltage VG By applying a gate voltage VG, a resonance tunnel effect can be realized.
  • the Majorana particles can move between two states with the tunnel effect. Therefore, by restoring the tunnel barrier at a desired timing, for example, an exchange 270 between a Majorana particle ⁇ 2 generated in the first region 171 and a Majorana particle ⁇ 5 generated in the second region 172 can be performed. That is, a quantum gate operation can be performed.
  • FIG. 20 is a diagram illustrating an example of the operation of the quantum bit circuit according to the second embodiment.
  • circles in FIG. 20 indicate Majorana particles in the regions 171 to 178 .
  • a line segment indicated by a broken line indicates that an s-wave superconductor layer is in a state where the Majorana particles cannot be exchanged
  • a line segment indicated by a solid line indicates that the s-wave superconductor layer is in a state where the Majorana particles can be exchanged.
  • the Majorana particle can be exchanged through charging.
  • the Majorana particles can be exchanged with the tunnel effect through control of the gate voltage, in addition to the exchange of the Majorana particles through charging.
  • the Majorana particles are exchanged between the first region 171 and the second region 172 , for example.
  • the Majorana particle ⁇ 2 generated in the first region 171 and the Majorana particle generated in the second region 172 are exchanged through a tunnel of the semiconductor layer 250 .
  • the Majorana particles are exchanged between the two fifth regions 175 adjacent to each other with the first region 171 interposed therebetween in the X-axis direction.
  • a Majorana particle ⁇ 1 generated in one fifth region 175 and a Majorana particle ⁇ 4 generated in another fifth region 175 are exchanged via a Majorana particle ⁇ 2 generated in the first region 171 between these fifth regions 175 through charging.
  • FIGS. 21 to 29 are diagrams illustrating the method for manufacturing the quantum bit circuit according to the second embodiment.
  • the lower s-wave superconductor layer 131 is formed on the substrate 110 .
  • the lower s-wave superconductor layer 131 can be formed by a deposition method, for example.
  • the lower electrode 251 is formed on the substrate 110 .
  • the lower electrode 251 can be formed by the deposition method, for example.
  • the plurality of lower Majorana carriers 121 is formed as in the first embodiment.
  • an etching stopper 241 X is provided so as to cover the lower Majorana carrier 121 , on the substrate 110 .
  • the etching stopper 241 X can be provided, for example, by separately growing the etching stopper 241 X on a growth substrate (not illustrated) and transferring the etching stopper 241 X from the growth substrate.
  • the etching stopper 241 X is an example of a first etching stopper.
  • a semiconductor layer 250 X is provided on the etching stopper 241 X.
  • the semiconductor layer 250 X can be provided, for example, by separately growing the semiconductor layer 250 X on a growth substrate (not illustrated) and transferring the semiconductor layer 250 X from the growth substrate.
  • the plurality of semiconductor layers 250 is formed.
  • the RIE is performed.
  • etching gas for example, fluorocarbon gas is used.
  • the lower Majorana carrier 121 is protected by the etching stopper 241 X.
  • the etching stopper 241 is formed between the lower Majorana carrier 121 and the semiconductor layer 250 .
  • the RIE is performed.
  • As etching gas for example, oxygen gas is used.
  • an etching stopper 242 X is provided so as to cover the lower Majorana carrier 121 and the semiconductor layer 250 , above the substrate 110 .
  • the etching stopper 242 X can be provided, for example, by separately growing the etching stopper 242 X on a growth substrate (not illustrated) and transferring the etching stopper 242 X from the growth substrate.
  • the etching stopper 242 X is an example of a second etching stopper.
  • a two-dimensional topological insulator layer 122 X is provided on the etching stopper 242 X.
  • the two-dimensional topological insulator layer 122 X can be provided, for example, by separately growing the two-dimensional topological insulator layer 122 X on a growth substrate (not illustrated) and transferring the two-dimensional topological insulator layer 122 X from the growth substrate.
  • the two-dimensional topological insulator layer 122 X may be formed on the etching stopper 242 X.
  • the plurality of upper Majorana carriers 122 is formed.
  • the RIE is performed.
  • etching gas for example, fluorocarbon gas is used.
  • the lower Majorana carrier 121 is protected by the etching stopper 242 X.
  • the etching stopper 242 is formed between the semiconductor layer 250 and the upper Majorana carrier 122 .
  • the RIE is performed.
  • As etching gas for example, oxygen gas is used.
  • the lower s-wave superconductor layer 132 is formed on the lower Majorana carrier 121
  • the upper s-wave superconductor layer 133 is formed on the upper Majorana carrier 122
  • the upper electrode 252 is formed on the upper Majorana carrier 122 .
  • the upper electrode 252 can be formed, for example, by the deposition method.
  • the quantum bit circuit 2 according to the second embodiment can be manufactured.
  • FIG. 30 is a partially transparent top view illustrating the quantum bit circuit according to the third embodiment.
  • FIGS. 31 to 34 are cross-sectional diagrams illustrating the quantum bit circuit according to the third embodiment.
  • FIG. 31 corresponds to a cross-sectional diagram taken along a line XXXI-XXXI in FIG. 30 .
  • FIG. 32 corresponds to a cross-sectional diagram taken along a line XXXII-XXXII in FIG. 30 .
  • FIG. 33 corresponds to a cross-sectional diagram taken along a line XXXII-XXXIII in FIG. 30 .
  • FIG. 34 corresponds to a cross-sectional diagram taken along a line XXXIV-XXXIV in FIG. 30 .
  • a quantum bit circuit 3 includes a substrate 310 , a lower Majorana carrier 321 extending in the X-axis direction, and an upper Majorana carrier 322 extending in the Y-axis direction.
  • the substrate 310 is, for example, a semiconductor substrate such as a GaAs substrate or an InP substrate of which a plane direction of a surface is (100).
  • the X-axis direction and the Y-axis direction are directions orthogonal to the Z-axis direction perpendicular to the surface of the substrate 310 .
  • the Y-axis direction intersects with the X-axis direction, and for example, the X-axis direction and the Y-axis direction are orthogonal to each other.
  • the lower Majorana carrier 321 is a semiconductor nanowire, for example, including InAs.
  • the plurality of lower Majorana carriers 321 is arranged side by side in the Y-axis direction.
  • the lower Majorana carrier 321 is an example of a first Majorana carrier.
  • the upper Majorana carrier 322 is a semiconductor nanowire, for example, including InAs.
  • the plurality of upper Majorana carriers 122 is arranged side by side in the X-axis direction.
  • the upper Majorana carrier 322 is an example of a second Majorana carrier.
  • a buffer layer 381 and an underlying semiconductor layer 382 are provided on the substrate 310 .
  • the buffer layer 381 is an In1-xAlxAs layer of which the thickness is about one ⁇ m, and an Al composition x may change so as to be lattice-matched with the substrate 310 and the underlying semiconductor layer 382 , from an interface with the substrate 310 to an interface with the underlying semiconductor layer 382 .
  • the underlying semiconductor layer 382 is an In0.81Ga0.19As layer of which the thickness is about four nm.
  • the lower Majorana carrier 321 is formed on the underlying semiconductor layer 382 .
  • the thickness of the lower Majorana carrier 321 is, for example, about five nm.
  • a barrier layer 383 is formed on the underlying semiconductor layer 382 so as to cover the lower Majorana carrier 321 .
  • the barrier layer 383 is an In0.9Al0.1As layer of which the thickness is about five nm, on the lower Majorana carrier 321 .
  • the lower Majorana carrier 321 is covered with the barrier layer 383 and functions as a quantum well.
  • the upper Majorana carrier 322 is formed on the barrier layer 383 .
  • the thickness of the upper Majorana carrier 322 is, for example, about five nm.
  • a barrier layer 384 is formed on the barrier layer 383 so as to cover the upper Majorana carrier 322 .
  • the barrier layer 384 is an In0.9Al0.1As layer of which the thickness is about five nm on the upper Majorana carrier 322 .
  • the upper Majorana carrier 322 is covered with the barrier layer 384 and functions as a quantum well.
  • an opening portion 391 reaching the underlying semiconductor layer 382 is formed in the barrier layers 383 and 384 , in the vicinity of the lower Majorana carrier 321 in plan view, and a lower s-wave superconductor layer 331 is provided in the opening portion 391 .
  • the lower s-wave superconductor layer 331 is, for example, an Al layer.
  • the lower s-wave superconductor layer 331 is an example of a first s-wave superconductor layer.
  • an opening portion 392 reaching the barrier layer 383 is formed in the barrier layer 384 , in the vicinity of the upper Majorana carrier 322 in plan view, and an upper s-wave superconductor layer 332 is provided in the opening portion 392 .
  • the upper s-wave superconductor layer 332 is, for example, an Al layer.
  • the upper s-wave superconductor layer 332 is an example of a second s-wave superconductor layer.
  • an opening portion 393 reaching the lower Majorana carrier 321 is formed in the barrier layers 383 and 384 , and a lower electrode 351 is formed in the opening portion 393 .
  • an upper electrode 352 is formed on the barrier layer 384 in a region where the lower Majorana carrier 321 and the upper Majorana carrier 322 overlap in plan view.
  • a power supply 353 is provided that applies a voltage between the single lower electrode 351 and the single upper electrode 352 adjacent to each other in the X-axis direction. The power supply 353 is provided for each pair of the lower electrode 351 and the upper electrode 352 .
  • the Majorana particles can exist in a portion of the lower Majorana carrier 321 overlapping the upper Majorana carrier 322 in plan view and a portion of the upper Majorana carrier 322 overlapping the lower Majorana carrier 321 in plan view. Then, for example, in these portions where the Majorana particles can exist, the portion of the lower Majorana carrier 321 overlapping the upper Majorana carrier 322 in plan view functions as a first region 371 , and the portion of the upper Majorana carrier 322 overlapping the lower Majorana carrier 321 in plan view functions as a second region 372 .
  • the Majorana particles can be exchanged between the two first regions 371 adjacent to each other in the X-axis direction.
  • the Majorana particles can be exchanged between the two second regions 372 adjacent to each other in the Y-axis direction.
  • the gate voltage to be applied from the power supply 353 the Majorana particles can be exchanged between the first region 371 and the second region 372 adjacent to each other in the Z-axis direction.
  • a graphene nanoribbon can be used as a Majorana carrier.
  • the quantum bit circuits 1 to 3 can be incorporated in a quantum computer 400 and used, for example, as a quantum bit circuit 401 .

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